The present invention relates to a rotating and driving system for a survey instrument.
To adjust collimating direction of a telescope on a survey instrument, the survey instrument is provided with a rotating and driving system for rotating a movable unit including the telescope. In recent years, motorized rotating and driving systems for driving movable unit by servomotor have been widely propagated.
Survey instruments are used at various places or under varied outdoor conditions such as in field or mountainous region, etc. The modes to carry or transport the survey instruments are also diverse, and the instruments are usually carried in portable cases so that they may not be damaged even when they are dropped and so on. On each of such carrying cases, a concave portion to match the shape of the instrument is formed, and the instrument is put in the concave portion to prevent loosening or rattling when it is carried in the case.
In the following, description will be given of a conventional type rotating and driving system for survey instrument referring to FIGS. 7 and 8.
In the figures, reference numeral 1 represents a movable unit where telescope and other components are furnished, 2 is a housing for rotatably supporting the movable unit 1, and a rotating and driving system 3 is accommodated in the housing 2.
On both ends of the movable unit 1, shafts 4 and 5 are arranged and the rotating and driving system 3 is connected to one of the shafts 4, and an encoder 6 for detecting rotating angle of the movable unit 1 is disposed on the shaft 5.
Description is given now on the rotating and driving system 3.
In the housing 2, a motor 8 is arranged in parallel with the axis of the rotating shaft of the movable unit 1 via a support 7, and a driving gear 9 is engaged with the output shaft of the motor 8. An idle shaft 10 is rotatably provided on the housing 2. A large diameter reduction gear 11 and a small diameter reduction gear 12 are fixedly mounted on the idle shaft 10, and the large diameter reduction gear 11 is engaged with the driving gear 9. On the shaft 4, a driven gear wheel 13 having a diameter larger than that of the small diameter reduction gear 12 is arranged. The driven gear wheel 13 is engaged with the small diameter reduction gear 12. Rotation of the driving gear 9 is reduced via the large diameter reduction gear 11, the small diameter reduction gear 12, and the driven gear wheel 13, and the rotation is transmitted to the movable unit 1.
By driving the motor 8, the movable unit 1 can be rotated at any angle desired.
As described above, the rotating and driving system of the survey instrument transmits the rotation of the motor 8 to the movable unit 1 via train of gears. In order to accurately transmit the rotation of the motor 8 to the movable unit 1 and to achieve positioning at high precision, backlash among each gear of the gear train should be as small as possible. In actual condition, however, pitch error, tooth profile error, tooth space runout, or lead error occur unavoidably in the manufacture of gears, and backlash among gears must be allowed to some extent for smooth rotation of gears. Therefore, there is some limitations in improving positioning accuracy of the movable unit 1 in the conventional type rotating and driving system for survey instrument.
As described above, a concave portion to match the shape of the survey instrument is formed in the carrying case, and the survey instrument is put in the concave portion in the carrying case so that it may not totter or wobble within the case. However, the movable unit 1 is often moved and tilted during survey operation, and its position does not always match the concave portion of the carrying case. Accordingly, the position of the movable unit 1 must be corrected to match the concave portion of the carrying case. For this reason, in a conventional type rotating and driving unit it is customary to drive the motor 8 and to correct the position of the movable unit 1 to the condition suitable to accommodate the concave portion of the carrying case.